Air circulation is awful in the (smaller) Tube trains. I read somewhere that the tunnels heat up so much during the day because of heat from the trains that the

Air circulation is awful in the (smaller) Tube trains. I read somewhere that the tunnels heat up so much during the day because of heat from the trains that they don’t have time to cool down at night. Definitely unpleasant in the summer. The larger trains are getting fitted with air conditioning nowadays.